At the present time, creosote is collected as a by-product during the distillation of coal tar to produce pitch. This creosote is a valuable by-product and is sold into the woodtreating industry as a perservative for treating wood to be used as railroad crossties, telephone poles, pilings, and many other end uses.
Creosote, as it is presently made, sold, and used, contains materials which will settle out as salts as the temperature decreases. Examples of these salt materials are, anthracene, phenanthrene, fluoranthene, and carbazole. The lower the temperature, and the longer the time that the creosote remains at lower temperatures, the more salts that form and settle. It is possible to remove most of these salts by cooling and filtering, but the market for such salts is limited and their value is such that the cost of recovery usually exceeds their worth. For this reason, the salts are normally left in the creosote oil. Additionally, it is felt by some that these materials add to the value of the creosote as a preservative; and therefore, should be retained in the creosote. In any case, these salts are seldom separated and recovered in the United States today, although in Europe, anthracene is still commercially recovered.
When these salts form and settle from the creosote, a sludge heel is formed which is difficult to put back into solution and also difficult to manage from a disposal aspect. Although it is possible to force the salt heel back into solution with sufficient expenditure of energy, perhaps aided by agitation, it is generally not cost effective to do so. Therefore, storage tanks of creosote are generally maintained at a temperature hot enough to prevent at least most of the salt formation. This temperature which inhibits salt formation is typically in the range of 180.degree. F. to 200.degree. F. (82.degree.-93.degree. C.) and is maintained by the supplier as well as by the customer for the most part. The energy required to maintain these temperatures to prevent this salting out is significant and represents a substantial portion of both the suppliers' and the customers' cost of operation. Even with the current practice of heating the tanks, sludge heels form over a period of time and these deposits must be periodically removed from the storage tanks. This cleaning of the tanks is generally done manually and is expensive due to the difficulty of removal. In addition, the sludge is classified environmentally as hazardous and it must be disposed of as hazardous waste. Such disposal is expensive.
In addition to the problem with slude heels in storage tanks, a similar problem occurs in railcars or barges when creosote is shipped via rail or water. Even though the creosote is loaded hot, the oil cools in transit and salt heels form. Upon receipt of the barges and railcars, the oil is heated, generally by steam or hot oil. Despite the expenditure of much energy, part of the heel usually remains in the barges and railcars after unloading. If the vessel is not cleaned after each trip, the heel quickly grows, thus reducing the effective volume of the vessel and thereby increasing the transportation cost per gallon of oil unloaded. It is thus apparent that a need exists for a creosote which is stable and does not settle out and which does not require its being maintained at an elevated temperature to preclude formation of sludge heels.